Preventing hydrate formation in a flowline

ABSTRACT

A water content sensor is positioned within a flowline downstream of a well-choke. The water content sensor is configured to determine a water content percentage of a production fluid flowing through the flowline. A temperature sensor is positioned downstream of the well-choke. The temperature sensor is configured to determine a temperature of the production fluid flowing through the flowline. A heating-jacket surroundings at least a portion of the flowline. The heating-jacket is configured to transfer heat into the flowline. A controller is configured to receive a signal from each of the water content sensor and the temperature sensor, and control the heating jacket in response to a signal from each of the water content sensor and the temperature sensor.

TECHNICAL FIELD

This disclosure relates to using heat jackets for preventing hydrateformation, for example, in flowlines through which fluids, for example,production fluids, flow.

BACKGROUND

Hydrates are solid crystalline compounds of snow-like appearance withdensities less than that of ice. Natural gas hydrates are formed whennatural gas components, for instance, methane, ethane, propane,isobutene, hydrogen sulfide, carbon dioxide, and nitrogen, occupy emptylattice positions in the water structure. In some instances, hydrateformation occurs at temperatures considerably higher than the freezingpoint of water. Gas hydrates constitute a solid solution, gas being thesolute and water the solvent, where the two main constituents are notchemically bounded.

Hydrates form at specific temperature and pressure ranges that aredependent on the ratio of hydrocarbons to water and the type ofhydrocarbons present. Flow assurance models are often run and analyzedto ensure that hydrate formation does not occur at a productionfacility.

SUMMARY

This disclosure describes technologies relating to preventing hydrateformation in a flowline.

An example implementation of the subject matter described within thisdisclosure is a system with the following features. A water contentsensor is positioned within a flowline downstream of a well-choke. Thewater content sensor is configured to determine a water contentpercentage of a production fluid flowing through the flowline. Atemperature sensor is positioned downstream of the well-choke. Thetemperature sensor is configured to determine a temperature of theproduction fluid flowing through the flowline. A heating-jacketsurroundings at least a portion of the flowline. The heating-jacket isconfigured to transfer heat into the flowline. A controller isconfigured to receive a signal from each of the water content sensor andthe temperature sensor, and control the heating jacket in response to asignal from each of the water content sensor and the temperature sensor.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The heating jacket include electric heaters.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The electric heaters include inductive heaters.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The electric heaters include direct current heaters.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The heating jacket is configured to deliver at least five megawatts ofheating into the flowline.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The heating jacket substantially covers at least one hundred feet of theflowline.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The heating jacket comprises a multiple sub-heat jackets.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The temperature sensor includes a distributed temperature sensorconfigured to determine a temperature profile along a length of theflowline.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following. Apressure sensor is positioned within the flowline downstream of awell-choke. The pressure sensor is configured to detect a pressurewithin the flowline.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The controller is configured to receive a signal from the pressuresensor. The controller is configured to control the heating jacket inresponse to the signal from the pressure signal.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The controller is configured to determine a water content threshold of aproduction fluid flowing through the flowline in response to the signalreceived from the water content sensor. The controller is configured todetermine that a flowline temperature downstream of the well-chokedecreases to be less than a first specified temperature based on thesignal received from the temperature sensor. The controller isconfigured to activate a heating jacket in response to determining thatthe flowline temperature is less than the first specified temperature.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The controller is further configured to open a well-choke configured tothrottle production of a well.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The controller is further configured to determine that a flowlinetemperature downstream of the well-choke increases to be greater than asecond specified temperature, that is equal to or greater than the firstspecified temperature, based on the signal received from the temperaturesensor, and deactivate the heating jacket in response to determiningthat the flowline temperature is greater than the second specifiedtemperature.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The water content threshold is greater than five percent water contentby weight.

An example implementation of the subject matter described within thisdisclosure is a method with the following features. A water content of aproduction fluid flowing through an open well-choke is determined to begreater than a specified percentage. A flowline temperature downstreamof the well-choke is determined to decrease to be below a firstspecified temperature. A heating jacket is activated in response todetermining that the flowline temperature is less than the firstspecified temperature. A flowline temperature downstream of thewell-choke is determined to increase to be greater than a secondspecified temperature that is equal to or greater than the firstspecified temperature. The heating jacket is deactivated in response todetermining that the flowline temperature is greater than the secondspecified temperature.

Aspects of the example method, which can be combined with the examplemethod alone or in combination, include the following. A well-chokeconfigured to throttle production of a well is opened.

Aspects of the example method, which can be combined with the examplemethod alone or in combination, include the following. A pressure withinthe flowline is determined in response to a signal from a pressuresensor. A heating jacket is activated in response to the determinedpressure.

Aspects of the example method, which can be combined with the examplemethod alone or in combination, include the following, a pressure withinthe flowline is determined in response to a signal from a pressuresensor. A heating jacket is deactivated in response to the determinedpressure.

Aspects of the example method, which can be combined with the examplemethod alone or in combination, include the following. The specifiedpercentage is five percent.

Aspects of the example method, which can be combined with the examplemethod alone or in combination, include the following. Determining atemperature includes using a distributed temperature sensor.

Aspects of the example method, which can be combined with the examplemethod alone or in combination, include the following. Activating theheating jacket includes directing an electrical current through heatelements within the heating jacket.

Aspects of the example method, which can be combined with the examplemethod alone or in combination, include the following. The current is adirect current.

Aspects of the example method, which can be combined with the examplemethod alone or in combination, include the following. The heatingelements include inductive heating elements.

An example implementation of the subject matter described within thisdisclosure is a controller with one or more processors and anon-transitory computer-readable storage medium coupled to the one ormore processors and storing programming instructions for execution bythe one or more processors. The programming instructions instruct theone or more processors to open a well-choke configured to throttleproduction of a well. The programming instructions instruct the one ormore processors to determine that a water content of a production fluidflowing through the open well-choke is greater than five percent inresponse to a signal received from a water content sensor. Theprogramming instructions instruct the one or more processors todetermine that a flowline temperature downstream of the well-chokedecreases to be less than a first specified temperature in response to asignal received from a temperature sensor. The programming instructionsinstruct the one or more processors to activate a heating jacket inresponse to determining that the flowline temperature is less than thefirst specified temperature. The programming instructions instruct theone or more processors to determine that a flowline temperaturedownstream of the well-choke increases to be greater than a secondspecified temperature that is equal to or greater than the firstspecified temperature in response to a signal received from thetemperature sensor. The programming instructions instruct the one ormore processors to deactivate the heating jacket in response todetermining that the flowline temperature is greater the secondspecified temperature.

The details of one or more implementations of the subject matterdescribed in this disclosure are set forth in the accompanying drawingsand the description. Other features, aspects, and advantages of thesubject matter will become apparent from the description, the drawings,and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example hydrate prevention system.

FIG. 2 is a chart of an example hydrate forming region and non-hydrateforming region.

FIG. 3 is a flowchart of an example method that can be used with aspectsof this disclosure.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

Hydrate formation within a flowline can temporarily stop productionthrough the flowline. In the context of this disclosure, the “flowline”is a piping section between a wellhead-choke and a production manifold.However, aspects of this disclosure are applicable to any pipe carryingfluid from one position to another. In general, this disclosure assumesa metallic flowline, but other flowline materials can be used withoutdeparting from the scope of this disclosure. Flow assurance models canbe run to determine what well-flow scenarios can result in hydrateformation, but some flow scenarios may not be avoidable, particularly,if the scenario includes start-up or shut-down conditions. Duringstart-up and shut-down operations, a wellhead choke creates a largepressure drop within the flowline. Such a pressure drop can result inJoule-Thomson effect cooling that can decrease the temperature offlowing well-flow into a hydrate forming range.

This disclosure relates to a system and method to prevent hydrateformation in the flowline by minimizing a temperature drop resultingfrom the Joule-Thomson effect across the pipeline. The system includeselectric heating jackets installed around a flowline immediatelydownstream of the choke. The electric heating jackets are activated whenthere is a high probability of hydrate formation. The threshold for a“high probability” can be determined by the end user. For example, insome instances, a 10% chance ca be considered a high probability. Insome instances, a 50% chance is considered a high probability. Theprobability of hydrate formation is determined based on the temperature,the water content, and the pressure of the gas going through the choke.

FIG. 1 shows an example hydrate prevention system 100. The hydrateprevention system 100 includes a water content sensor 102 positionedwithin a flowline 104 downstream of a well-choke 106.

The well-choke 106 is configured to throttle production of the well. Thewell-choke includes a specially designed valve and actuator. The valveis configured to allow a large pressure drop across the valve without“cutting” the valve, that is, the valve will resist deterioration due tocavitation or erosion. In some instances, the large pressure drop canrange from substantially 100 pounds per square inch (PSI) to severalthousand PSI. The actuator is configured to precisely control theposition of the valve based on production demands, that is, the actuatorcontrols how much the choke is opened and closed. A well-flow flow-rateis regulated based on the position of the valve and the resultingpressure drop across the valve due to the valve's position.

The water content sensor 102 is configured to determine a water contentpercentage of a production fluid flowing through the flowline 104. Thewater content sensor 102 is positioned within the flowline 104 anddownstream of the well-choke 106.

A temperature sensor 108 is positioned within or along the flowlinedownstream of the well-choke. The temperature sensor 108 is configuredto determine a temperature of the production fluid flowing through theflowline 104. In some implementations, the temperature sensor 108includes a distributed temperature sensor configured to determine atemperature profile along a length of the flowline 104. In someimplementations, the temperature sensor 108 can be positioned outside ofthe flowline 104. In some implementations, the temperature sensor 108can be positioned within the flowline. The temperature sensor 108 caninclude a thermocouple, calibrated spring, fiber optic line, or anyother temperature sensing device.

One or more pressure sensors 114 are positioned within the flowline 104downstream of a well-choke 106. The one or more pressure sensors 114 areconfigured to detect a pressure within the flowline 104. In someimplementations, a distributed pressure sensor can be used.

One or more heating jackets 110 surround at least a portion of theflowline 104. In some implementations, the heating jacket 110 can be aflexible blanket that can be wrapped around the flowline 104 and securedusing wire-ties or other securing mechanisms. In some instances, theheating jacket 110 is rigid and is configured to be secured around aspecific pipe size of the flowline 104. In such an implementation, theheating jacket 110 can be secured with a clamp, screw, or otherfastener. The heating jacket 110 is configured to transfer heating intothe flowline 104. In some implementations, the heating jacket 110 ispositioned close to the well choke 106, for example, as close aspossible with the present piping configuration. The heating jacket 110can include electric heaters or tubing through which a heated fluidflows. In the instance of an electric heater being used, the electricheater can include a direct current heater, an alternating currentheater, an inductive heater, a conductive heater, a radiant heater, anycombination of them, or any other type of electric heater. In someimplementations, a radiation heat jacket is used. Regardless of the typeof heating mechanism used, the heating jackets 110 are configured todeliver a large amount of heat, for example, five megawatts to tenmegawatts of heat, into the flowline. There are certain relationshipsthat can dictate how much heat is required by the system. For example, alarger diameter flowline 104 may require more heat than a smallerdiameter flowline. In some implementations, a flowline 104 thatexperiences a larger pressure drop will require more heat than aflowline 104 that experiences a smaller pressure drop. The pressure dropcan be affected by the diameter and length of the flowline 104. Theheating jackets 110 can substantially cover at least one hundred feet ofthe flowline 104 within plus or minus ten feet. In some instances, theheating jackets 110 can cover at least three hundred feet of theflowline 104. In some instances, the heating jacket 110 includesmultiple, smaller sub-heat jackets that can be interconnected to a powersupply in series or parallel. In the illustrated example, the one ormore heating jackets 110 includes three sub-heat jackets 110 a, 110 b,and 110 c. The sub-heat jackets can be wired together as a group to actas a single jacket. The gaps provided by the sub-heat jackets can createclearance for flanges or valves to protrude from the one or more heatingjackets 110. While the illustrated implementation includes threesub-jackets, any number of sub jackets can be used. The heating jackets110 can be permanent installations or temporary installations.

The system 100 also includes a controller 112 that is connected to thewater content sensor 102, the one or more heating jackets 110, thetemperature sensor 108, and one or more pressure sensors 114 that areconfigured to detect a pressure within the flowline 104. The controller112 is configured to receive a signal from the water content sensor 102,a signal from the temperature sensor 108, and a signal from the pressuresensor 114. The controller 112 is also configured to control, that is,activate, deactivate, or both, the heating jacket 110 in response to asignal from the water content sensor 102, the temperature sensor 108,the pressure sensor 114, or any combination. In some instances, thecontroller 112 can activate, deactivate, or both, the heating jacket 110in response to an operator input.

The controller 112 includes one or more processors and a non-transitorycomputer-readable storage medium coupled to the one or more processors.Additionally, the controller 112 includes an input/output (I/O) moduleconfigured to send and receive signals to and from the outside of thecontroller 112. For example, the I/O module can receive signals fromsensors, such as the temperature sensor 108, the pressure sensor 114, orwater content sensor 102. For Example, the I/O module can send a signalto activate the heating jackets 110. The non-transitory memory storesprogramming instructions for execution by the one or more processors.For example, the programming instructions can instruct the one or moreprocessors to do the following tasks.

In some instances, the I/O module of the controller 112 can open thewell-choke 106 by sending a signal to the actuator on the choke 106. Thecontroller 112 can determine that the water content of a productionfluid flowing through the open well-choke 106 is greater than aspecified threshold, stored in the non-transitory memory, in response toa signal received from the water content sensor 102. In some instances,the specified threshold can be a water content percentage, such as fivepercent. The signal from the water content sensor 102 can include acurrent, voltage, or hydraulic pressure that is interpreted by thecontroller 112 to be indicative of a water content value. For example,the specified threshold can be greater than or equal to five percent byweight of water.

The controller 112 can determine if a flowline pressure downstream ofthe well-choke 106 decreases to be less than a first specified pressurevalue, stored in the non-transitory memory, in response to a signalreceived from a pressure sensor 114. The specified pressure can be apressure value below which hydrate formation is likely. The signal fromthe pressure sensor 114 can include a current, voltage, or hydraulicpressure that is interpreted by the controller 112 to be indicative of apressure value. For example, a threshold pressure can be fiveMegapascals (Mpa) in some instances. The controller 112 can activate theheating jacket 110, that is, turn on the heating jacket, in response todetermining that the flowline 104 pressure is less than the firstspecified temperature. While the system 100 is primarily describedwithin this model as having a threshold-based control scheme, anycontrol scheme based on any flow assurance model can be used. Forexample, as shown in FIG. 2, a function of pressures and temperaturescan be used to plot a hydrate region 202 and a non-hydrate region 204.If the controller senses a pressure and temperature within the hydrateregion 202, then the heating jacket 110 is activated. If the pressureand temperature are in the non-hydrate region 204, then the heatingjacket 110 will be deactivated by the controller 112 ore remaininactive.

The controller 112 can determine if a flowline temperature downstream ofthe well-choke 106 decreases to be below a first specified temperaturevalue, stored in the non-transitory memory, in response to a signalreceived from a temperature sensor 108. The signal from the temperaturesensor 108 can include a current, voltage, or hydraulic pressure that isinterpreted by the controller 112 to be indicative of a temperaturevalue. For example, the threshold temperature can be 285 Kelvin (K) insome instances. The controller 112 can activate the heating jacket 110,that is, turn on the heating jacket, in response to determining that theflowline 104 temperature is less than the first specified temperature.While the system 100 is primarily described within this model as havinga threshold-based control scheme, any control scheme based on any flowassurance model can be used. For example, as shown in FIG. 2, a functionof pressures and temperatures can be used to plot a hydrate region 202and a non-hydrate region 204. If the controller senses a pressure andtemperature within the hydrate region 202, then the heating jacket 110is activated. If the pressure and temperature are in the non-hydrateregion 204, then the heating jacket 110 will be deactivated by thecontroller 112 or remain inactive. The controller 112 can determine thata flowline 104 temperature downstream of the well-choke 106 increases tobe greater than a second specified temperature value, stored in thenon-transitory memory, that is equal to or greater than the firstspecified temperature in response to a signal received from thetemperature sensor 108. The signal from the temperature sensor 108 caninclude a current, voltage, or hydraulic pressure that is interpreted bythe controller 112 to be indicative of a temperature value. For example,the second temperature can be greater than or equal to the firsttemperature in some instances. The controller 112 can deactivate theheating jacket 110 in response to determining that the flowline 104temperature is greater than the second specified temperature.

FIG. 3 is a flowchart of an example method 300 that can be used withaspects of this disclosure. At 302, the well-choke 106 configured tothrottle production of a well is opened. At 304, a water content of aproduction fluid flowing through the open well-choke 106 is determinedto be greater than a specified percentage. For example, the specifiedpercentage can be five percent water content by weight. At 306, aflowline temperature downstream of the well-choke 106 is determined todecrease to be less than a first specified temperature. Steps 304 and306 can occur simultaneously or in any sequence. At 308, a heatingjacket 110 is activated in response to determining that the flowlinetemperature is less than the first specified temperature. In someinstances, a pressure is determined within the flowline 104 in responseto a signal from the pressure sensor 114. In some instances, the heatingjacket 110 is activated in response to the determined pressure. At 310,a flowline 104 temperature downstream of the well-choke 106 isdetermined to increase to be greater than a second specified temperaturethat is equal to or greater than the first specified temperature. Insome instances, deactivation can be performed in response to a change inwater content, pressure, or both. At 312, the heating jacket 110 isdeactivated in response to determining that the flowline 104 temperatureis greater than the second specified temperature. In some instances, theheating jacket 110 is deactivated in response to the determinedpressure.

While this disclosure contains many specific implementation details,these should not be construed as limitations on the scope of what may beclaimed, but rather as descriptions of features specific to particularimplementations. Certain features that are described in this disclosurein the context of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresthat are described in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features may be previously describedas acting in certain combinations and even initially claimed as such,one or more features from a claimed combination can in some cases beexcised from the combination, and the claimed combination may bedirected to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, toachieve desirable results. Alternatively or additionally, not allillustrated operations may be required to be performed to achievedesirable results. Moreover, the separation of various system componentsin the implementations previously described should not be understood asrequiring such separation in all implementations, and it should beunderstood that the described program components and systems cangenerally be integrated together in a single product or packaged intomultiple products.

Thus, particular implementations of the subject matter have beendescribed. Other implementations are within the scope of the followingclaims. In some cases, the actions recited in the claims can beperformed in a different order and still achieve desirable results. Inaddition, the processes depicted in the accompanying figures do notnecessarily require the particular order shown, or sequential order, toachieve desirable results.

What is claimed is:
 1. A system comprising: a water content sensorpositioned within a flowline downstream of a well-choke, the watercontent sensor configured to determine a water content percentage of aproduction fluid flowing through the flowline; a temperature sensorpositioned downstream of the well-choke, the temperature sensorconfigured to determine a temperature of the production fluid flowingthrough the flowline; a heating jacket surrounding at least a portion ofthe flowline, the heating jacket configured to transfer heat into theflowline; and a controller configured to: receive a signal from each ofthe water content sensor and the temperature sensor, control the heatingjacket responsive to a signal from each of the water content sensor andthe temperature sensor; determine a water content threshold of aproduction fluid flowing through the flowline responsive to the signalreceived from the water content sensor; determine that a flowlinetemperature downstream of the well-choke decreases to be less than afirst specified temperature based on the signal received from thetemperature sensor; activate a heating jacket in response to determiningthat the flowline temperature is less than the first specifiedtemperature; determine that a flowline temperature downstream of thewell-choke increases to be greater than a second specified temperature,that is equal to or greater than the first specified temperature, basedon the signal received from the temperature sensor; and deactivate theheating jacket in response to determining that the flowline temperatureis greater than the second specified temperature.
 2. The system of claim1, wherein the heating jacket comprises electric heaters.
 3. The systemof claim 2, wherein the electric heaters comprise inductive heaters. 4.The system of claim 2, wherein the electric heaters comprise directcurrent heaters.
 5. The system of claim 1, wherein the heating jacket isconfigured to deliver at least five megawatts of heating into theflowline.
 6. The system of claim 1, wherein the heating jacketsubstantially covers at least one hundred feet of the flowline.
 7. Thesystem of claim 1, wherein the heating jacket comprises a plurality ofsub-heat jackets.
 8. The system of claim 1, wherein the temperaturesensor comprises a distributed temperature sensor configured todetermine a temperature profile along a length of the flowline.
 9. Thesystem of claim 1, further comprising a pressure sensor positionedwithin the flowline downstream of a well-choke, the pressure sensorconfigured to detect a pressure within the flowline.
 10. The system ofclaim 9, wherein the controller is configured to receive a signal fromthe pressure sensor, the controller being configured to control theheating jacket in response to the signal from the pressure sensor. 11.The system of claim 1, wherein the controller is further configured toopen a well-choke configured to throttle production of a well.
 12. Thesystem of claim 1, wherein the water content threshold is greater thanfive percent water content by weight.